Mechanical Effects of a Specific Neurodynamic Mobilization of the Superficial Fibular Nerve: A Cadaveric Study.

CONTEXT: A specific neurodynamic mobilization for the superficial fibular nerve (SFN) has been suggested in the reference literature for manual therapists to evaluate nerve mechanosensitivity in patients. However, no authors of biomechanical studies have examined the ability of this technique to produce nerve strain. Therefore, the mechanical specificity of this technique is not yet established. OBJECTIVES: To test whether this examination and treatment technique produced nerve strain in the fresh frozen cadaver and the contribution of each motion to total longitudinal strain. DESIGN: Controlled laboratory study. SETTING: Laboratory. MAIN OUTCOME MEASURE(S): A differential variable reluctance transducer was inserted in 10 SFNs from 6 fresh cadavers to measure strain during the mobilization. A specific sequence of plantar flexion, ankle inversion, straight-leg raise position, and 30° of hip adduction was applied to the lower limb. The mobilization was repeated at 0°, 30°, 60°, and 90° of the straight-leg raise position to measure the effect of hip-flexion position. RESULTS: Compared with a resting position, this neurodynamic mobilization produced a significant amount of strain in the SFN (7.93% ± 0.51%, P < .001). Plantar flexion (59.34% ± 25.82%) and ankle inversion (32.80% ± 21.41%) accounted for the biggest proportions of total strain during the mobilization. No difference was noted among different hip-flexion positions. Hip adduction did not significantly contribute to final strain (0.39% ± 10.42%, P > .05), although high variability among limbs existed. CONCLUSIONS: Ankle motion should be considered the most important factor during neurodynamic assessment of the SFN for distal entrapment. These results suggest that this technique produces sufficient strain in the SFN and could therefore be evaluated in vivo for correlation with mechanosensitivity.

A cadaveric study of ulnar nerve strain at the elbow associated with cubitus valgus/varus deformity.

BACKGROUND: Cubital tunnel syndrome can be caused by overtraction and dynamic compression in elbow deformities. The extent to which elbow deformities contribute to ulnar nerve strain is unknown. Here, we investigated ulnar nerve strain caused by cubitus valgus/varus deformity using fresh-frozen cadavers. METHODS: We used six fresh-frozen cadaver upper extremities. A strain gauge was placed on the ulnar nerve 2 cm proximal to the medial epicondyle of the humerus. For the elbow deformity model, osteotomy was performed at the distal humerus, and plate fixation was performed to create cubitus valgus/varus deformities (10°, 20°, and 30°). Ulnar nerve strain caused by elbow flexion (0-125°) was measured in both the normal and deformity models. The strains at different elbow flexion angles within each model were compared, and the strains at elbow extension and at maximum elbow flexion were compared between the normal model and each elbow deformity model. However, in the cubitus varus model, the ulnar nerve deflected more than the measurable range of the strain gauge; elbow flexion of 60° or more were considered effective values. Statistical analysis of the strain values was performed with Friedman test, followed by the Williams' test (the Shirley‒Williams' test for non-parametric analysis). RESULTS: In all models, ulnar nerve strain increased significantly from elbow extension to maximal flexion (control: 13.2%; cubitus valgus 10°: 13.6%; cubitus valgus 20°: 13.5%; cubitus valgus 30°: 12.2%; cubitus varus 10°: 8.3%; cubitus varus 20°: 8.2%; cubitus varus 30°: 6.3%, P < 0.001). The control and cubitus valgus models had similar values, but the cubitus varus models revealed that this deformity caused ulnar nerve relaxation. CONCLUSIONS: Ulnar nerve strain significantly increased during elbow flexion. No significant increase in strain 2 cm proximal to the medial epicondyle was observed in the cubitus valgus model. Major changes may have been observed in the measurement behind the medial epicondyle. In the cubitus varus model, the ulnar nerve was relaxed during elbow extension, but this effect was reduced by elbow flexion.

Assessing Sciatic Nerve Excursion and Strain with Ultrasound Imaging during Forward Bending.

Entrapment neuropathies affecting the sciatic nerve tract may adversely affect neural biomechanical features such as excursion and strain. There is a paucity of in vivo evidence examining the effects of forward bending upon sciatic nerve excursion and strain. The purpose of this study was to assess the reliability of ultrasound imaging in measuring sciatic nerve excursion and strain during forward bending movements. Secondary aims were to quantify sciatic nerve excursion and strain during forward bending movements and to assess the relationship between sciatic nerve excursion and movements of the hip and lumbar spine. The reliability of measuring sciatic nerve excursion was high to excellent whilst measurement of sciatic nerve strain was moderate. The amount of hip flexion, during forward bending, was a strong predictor of sciatic nerve excursion. These findings will support clinicians in the assessment and treatment of entrapment neuropathies, in addition to providing a foundation for future research.

Does the L5 spinal nerve move? Anatomical evaluation with implications for postoperative L5 nerve palsy.

PURPOSE: While palsy of the L5 nerve root due to stretch injury is a known complication in complex lumbosacral spine surgery, the underlying pathophysiology remains unclear. The goal of this cadaveric study was to quantify movement of the L5 nerve root during flexion/extension of the hip and lower lumbar spine. METHODS: Five fresh-frozen human cadavers were dissected on both sides to expose the lumbar vertebral bodies and the L5 nerve roots. Movement of the L5 nerve root was tested during flexion and extension of the hip and lower lumbar spine. Four steps were undertaken to characterize these movements: (1) removal of the bilateral psoas muscles, (2) removal of the lumbar vertebral bodies including the transforaminal ligaments from L3 to L5, (3) opening and removing the dura mater laterally to visualize the rootlets, and (4) removal of remaining soft tissue surrounding the L5 nerve root. Two metal bars were inserted into the sacral body at the level of S1 as fixed landmarks. The tips of these bars were connected to make a line for the ruler that was used to measure movement of the L5 nerve roots. Movement was regarded as measurable when there was an L5 nerve excursion of at least 1 mm. RESULTS: The mean age at death was 86.6 years (range 68-89 years). None of the four steps revealed any measurable movement after flexion/extension of the hip and lower lumbar spine on either side (< 1 mm). Flexion of the hip and lower lumbar spine revealed lax L5 nerve roots. Extension of the hip and lower lumbar spine showed taut ones. CONCLUSION: Significant movement or displacement of the L5 nerve root could not be quantified in this study. No mechanical cause for L5 nerve palsy could be identified so the etiology of the condition remains unclear.

Adduction-Induced Strain on the Optic Nerve in Primary Open Angle Glaucoma at Normal Intraocular Pressure.

PURPOSE/AIM: The optic nerve (ON) becomes taut during adduction beyond ~26° in healthy people and patients with primary open angle glaucoma (POAG), but only retracts the globe in POAG. We used magnetic resonance imaging (MRI) to investigate this difference. MATERIALS AND METHODS: MRI was obtained in 2-mm quasi-coronal planes in central gaze, and smaller (~23-25°) and larger (~30-31°) adduction and abduction in 21 controls and 12 POAG subjects whose intraocular pressure never exceeded 21 mmHg. ON cross-sections were analyzed from the globe to 10 mm posteriorly. Area centroids were used to calculate ON path lengths and changes in cross-sections to calculate elongation assuming volume conservation. RESULTS: For both groups, ON path was nearly straight (<102.5% of minimum path) in smaller adduction, with minimal further straightening in larger adduction. ON length was redundant in abduction, exceeding 103% of minimum path for both groups. For normals, the ON elongated 0.4 ± 0.5 mm from central gaze to smaller adduction, and 0.4 ± 0.5 mm further from smaller to larger adduction. For POAG subjects, the ON did not elongate on average from central gaze to smaller adduction and only 0.2 ± 0.4 mm from smaller to larger adduction (P = .045 vs normals). Both groups demonstrated minimal ON elongation not exceeding 0.25 mm from central gaze to smaller and larger abduction. The globe retracted significantly more during large adduction in POAG subjects than normals (0.6 ± 0.7 mm vs 0.2 ± 0.5 mm, P = .027), without appreciable retraction in abduction. For each mm increase in globe axial length, ON elongation in large adduction similarly increased by 0.2 mm in each group. CONCLUSIONS: The normal ON stretches to absorb force and avert globe retraction in adduction. In POAG with mild to severe visual field loss, the relatively inelastic ON tethers and retracts the globe during adduction beyond ~26°, transfering stress to the optic disc that could contribute to progressive neuropathy during repeated eye movements.

Shoulder position increases ulnar nerve strain at the elbow of patients with cubital tunnel syndrome.

BACKGROUND: Previous studies have shown that the shoulder internal rotation elbow flexion (SIREF) test, which is a modified elbow flexion (EF) test, has significantly higher sensitivity than the EF test in patients with cubital tunnel syndrome (CubTS). Here, we hypothesized that this increase in sensitivity was due to increase in the ulnar nerve strain around the elbow introduced by the additional shoulder position. METHODS: Ulnar nerve strain at the elbow was intraoperatively measured at both the EF test and SIREF test positions in 20 patients with CubTS before simple decompression. Statistical analysis was performed with the Wilcoxon signed rank test at a confidence level of 99% (P < .001). RESULTS: Mean ulnar nerve strain in the EF test position was 18.9% ± 12.1%, whereas that in the SIREF test position was 24.7% ± 14.0%. Ulnar nerve strain was higher in the SIREF than in the EF test position in all cases, and the difference was significant (mean, 5.8% ± 0.9%; 95% confidence interval, 3.90%-7.73%). CONCLUSION: This study indicated that increased sensitivity in the SIREF test compared with the EF test was due to the increase in ulnar nerve strain around the elbow. To the best of our knowledge, this is the first study showing that shoulder position changes the ulnar nerve strain around the elbow in living patients with CubTS.

Associations between ulnar nerve strain and accompanying conditions in patients with cubital tunnel syndrome.

Pathophysiology of cubital tunnel syndrome (CubTS) is still controversial. Ulnar nerve strain at the elbow was measured intraoperatively in 13 patients with CubTS before simple decompression. The patients were divided into three groups according to their accompanying conditions: compression/adhesion, idiopathic, and relaxation groups. The mean ulnar nerve strain was 43.5 ± 30.0%, 25.5 ± 14.8%, and 9.0 ± 5.0% in the compression/adhesion, idiopathic, and relaxation groups respectively. The mean ulnar nerve strains in patients with McGowan's classification grades I, II, and III were 18.0 ± 4.2%, 27.1 ± 22.7%, and 33.7 ± 24.7%, respectively. The Jonckheere-Terpstra test showed that there were significant reductions in the ulnar nerve strain among the first three groups, but not in the three groups according to McGowan's classification. Our results suggest that the pathophysiology, not disease severity, of CubTS may be explained at least in part by the presence of ulnar nerve strain.